Use py2.4 compat string formatting in github_key (#2633)

Replace the use of python 2.6+ string .format() method
use with the python 2.4 compatible '%s' formatting to
make the github_key module py2.4 compatible.

source_control/github_key.py

@@ -99,7 +99,7 @@ class GitHubSession(object):
 
     def request(self, method, url, data=None):
         headers = {
-            'Authorization': 'token {}'.format(self.token),
+            'Authorization': 'token %s' % self.token,
             'Content-Type': 'application/json',
             'Accept': 'application/vnd.github.v3+json',
         }
@@ -147,7 +147,7 @@ def delete_keys(session, to_delete, check_mode):
         return
 
     for key in to_delete:
-        session.request('DELETE', API_BASE + '/user/keys/{[id]}'.format(key))
+        session.request('DELETE', API_BASE + '/user/keys/%s' % key[id])
 
 
 def ensure_key_absent(session, name, check_mode):